Macrophages, one of the major cell types in which HIV can both productively replicate and persist in a latent state, play a crucial role in HIV pathogenesis. In contrast to CD4+ T cells, macrophages are resistant to HIV-induced killing and have long lifespan. Indeed, macrophages appear to be an important reservoir and sustain high virus loads after depletion of CD4+ T cells in AIDS patients and in highly pathogenic SHIV- infected rhesus macaques. Importantly, macrophages are the major source of HIV during opportunistic infections, which occur more frequently during the advanced stages of AIDS. Because the long-lived HIV reservoirs constitute a major obstacle to HIV eradication, understanding the cellular and molecular mechanisms underlying HIV-macrophage interactions is vital for developing novel and efficacious therapeutic strategies against HIV and the AIDS epidemic. Susceptibility of primary macrophages to HIV depends on the anatomical location and activation state of the cells. Experimental investigation of the interactions between HIV-1 and macrophages has been impeded by the difficulty of isolating a large amount of human primary macrophages. We recently demonstrate that peritoneal macrophages (PMs) are highly abundant in ascitic fluid of patients with cirrhosis and are susceptible to HIV-1 infection. These cells are long-lived in vitro and can be cryopreserved. Freshly isolated PMs are susceptible to HIV R5, X4, X4R5 primary isolates by not but not to X4-T cell line adapted (TCLA) strains. Interestingly, after 7 days in culture, PMs acquired susceptibility to X4-TCLA strains and produced greater amounts of primary X4 and X4R5 HIV than freshly-isolated PMs. Concurrently, the level of CXCR4 mRNA and production of CC-chemokines increased significantly during 7 days in culture, suggesting that an increase in levels of HIV-coreceptors and CC-chemokines may contribute to the susceptibility to X4-TCLA and enhanced viral production of X4-ultizing isolates, respectively. HIV coreceptor switch from R5 to X4 has been associated with rapid CD4+ T cell loss and progression of AIDS when macrophages are the major source of HIV. Although the basis for HIV co-receptor switch is attributed to the complex interaction of the viral population with various cell populations of the immune system, the contribution by macrophages to HIV co-receptor switch is not known. Our long-term goal is to determine whether macrophages serve as an important reservoir and whether they play a role in HIV-coreceptor switch at the late stage of disease progression. Thus, further characterization of HIV-peritoneal macrophage interactions will offer an important insight into the role of macrophages in HIV pathogenesis. The goal of this proposal is to dissect the underlying mechanisms of dynamic HIV co-receptor usages in PMs and to amplify and characterize HIV envelopes from peritoneal macrophages from HIV-infected individuals. The outcome of this study will enhance our understanding of the role of macrophages in HIV pathogenesis and may facilitate discoveries of new ways for treatment. PUBLIC HEALTH RELEVANCE: The goal of this proposal is to dissect the underlying mechanisms of dynamic HIV co-receptor usages in PMs and to characterize HIV Env in PMs from HIV-infected patients.